what the heck is poppy's damage coming form?

Well I mean, top lane Poppy builds like three damage items most of the time (BC, Gage, IBG). I've never seen a Poppy do significant damage that wasn't building damage items.

「 INITIAL PHYSICAL DAMAGE: 40 / 70 / 100 / 130 / 160 (+ 70% bonus AD) (+ 6% of target's max. health) 」 That's her q damage, and it deals the same thing again on the second part, so if you get hit with both parts you're taking 12% maxhp + all the base dmg.

You DO know what her Q does, right?

her overtuned Q.

It's important to also note that the base damage on Q is more than 6% of a targets max health if they have less than ~2600 HP, so a rank 5 Q on just about any champion is >12% of their max health in physical damage every 4 or so seconds. Doubled if you can't move for one reason or another. That's just base damage on one ability without building any offensive items.

I actually started thinking the other day that Riot has gone overboard with Percent Health damage recently. Kindred, Fiora, Poppy, and Shen come to mind. I'm not against the idea of it, and it's kind of a good thing in the current meta. I still can't help but think there's been a bit too much lately and that it feels like it brings focus to champs who have it themselves as counter picks.

It's coming from the walls.

But seriously, that's where it's coming from. Poppy has like zero damage without a wall.

'Juggernaut' Poppy does do an absurd amount of damage while being virtually unkillable. I finally had the displeasure to facing one the other day. Early game was fine, but once Iceborn Gauntlet was completed I couldn't keep her in check in lane, and once she got her Deadmans Plate she quickly became a problem for the entire team. She does have her weaknesses, but she will definitely punish an unprepared team and is quite a lot stronger than I think I lot of people give her credit right now.